The combustor module of a modern aircraft gas turbine engine includes an annular combustor circumscribed by a case. The combustor includes radially inner and outer liners and a bulkhead extending radially between the forward ends of the liners. A series of openings penetrates the bulkhead. An air swirler with a large central opening occupies each bulkhead opening. A fuel injector bearing plate with a relatively small, cylindrical central opening is clamped against the swirler in a way that allows the bearing plate to slide or “float” relative to the swirler.
The combustor module also includes a fuel injector for supplying fuel to the combustor. The fuel injector has a stem secured to the case and projecting radially inwardly therefrom. A nozzle, which is integral with the stem, extends substantially perpendicularly from the stem and projects through the cylindrical opening in the bearing plate. The portion of the nozzle that projects through the bearing plate is cylindrical and has an outer diameter nearly equal to the diameter of the opening in the bearing plate.
During engine operation, combustion air enters the front end of the combustor by way of the air swirler. The swirler swirls the incoming air to thoroughly blend it with the fuel supplied by the fuel injector. The thorough blending helps minimize undesirable exhaust emissions from the combustor. The swirler also regulates the quantity of air delivered to the front end of the combustor. This is important because excessive air can extinguish the combustion flame, a problem known as lean blowout. Turbine engines are especially susceptible to lean blowout when operated at or near idle and/or when decelerated abruptly from high power. The aforementioned near-equivalent diameters of the fuel nozzle and the opening in the bearing plate help prevent air leakage that would make the combustor more vulnerable to lean blowout.
During engine operation, the components near the front end of the combustor, such as the air swirler and bulkhead, are exposed to high temperatures due to their proximity to the combustion flame. The fuel injector stem, and the case to which the stem is mounted, are exposed to relatively lower temperatures. The temperature differences cause these components to expand and contract differently, which displaces the fuel nozzle radially and/or circumferentially relative to the swirler. The fact that the bearing plate is slidably mounted to the swirler, as noted above, allows the bearing plate to slide and accommodate the displacement of the nozzle while continuing to prevent detrimental air leakage in the vicinity of the nozzle.
Although conventional bearing plates are effective at accommodating translational displacement of the nozzle relative to the swirler, they cannot readily accommodate changes in the angular orientation of the nozzle. For example, if thermal gradients, pressure loading or other influences cause the nozzle and/or the bulkhead to rotate about a laterally or radially extending axis, the nozzle and/or the central opening in the bearing plate can experience fretting wear. This wear can allow air leakage through the opening, which makes the combustor more susceptible to lean blowout. In extreme circumstances, the rotational movement can fracture the fuel nozzle. In addition, the rotational movement of the nozzle can pull the bearing plate away from the swirler (a phenomenon known as “burping”) which allows undesirable air leakage past the planar interface between the bearing plate and the swirler.
What is needed is a fuel injector bearing plate assembly and a swirler assembly that accommodate rotation of the fuel injector nozzle relative to the combustor hardware (for example the bulkhead and swirler).